High Volume vs Standard Volume Oil Pump

Easier than that. Slowly increase the revs on a warm engine. You'll see the oil pressure rise with RPM and then hold steady. This is the point where the pump is supplying more oil than the engine can use and the relief valve opens. On most healthy engines, this will occur below 3000 RPM.

If you use a stiffer relief valve spring, the valve won't open until a higher pressure/RPM. If you use a higher volume pump you'll just pump more oil back into the pan.